This invention pertains generally to internal combustion engine control systems, and more specifically to fluid-driven actuators on an engine.
Engine manufacturers are incorporating systems with fluid-driven actuators, including actuators driven by engine lubricating oil pumped from an engine oil pump. Systems that include such actuators include variable cam phasing, cylinder deactivation, and variable valve lift and duration, among others. A system uses an oil control valve to divert flow of pressurized engine oil to drive the actuator to accomplish a desired work output. By way of example, an oil control valve used in conjunction with a variable cam phaser is used to accomplish variable opening time of an intake or exhaust valve, relative to a position of a reciprocating piston. The system uses the oil control valve to control the flow of engine oil to the variable cam phaser that is attached to a camshaft of the engine, based upon a command from an engine controller. Distinct engine performance benefits that are realized from the use of variable cam phasing include an improvement in combustion stability at idle, improved airflow into the engine over a range of engine operations corresponding to improvements in engine performance, and improved dilution tolerance. This results in such benefits as improved fuel economy, improved torque at low engine speeds, lower engine cost and improved quality through elimination of
This invention pertains generally to internal combustion engine control systems, and more specifically to fluid-driven actuators on an engine.
Engine manufacturers are incorporating systems with fluid-driven actuators, including actuators driven by engine lubricating oil pumped from an engine oil pump. Systems that include such actuators include variable cam phasing, cylinder deactivation, and variable valve lift and duration, among others. A system uses an oil control valve to divert flow of pressurized engine oil to drive the actuator to accomplish a desired work output. By way of example, an oil control valve used in conjunction with a variable cam phaser is used to accomplish variable opening time of an intake or exhaust valve, relative to a position of a reciprocating piston. The system uses the oil control valve to control the flow of engine oil to the variable cam phaser that is attached to a camshaft of the engine, based upon a command from an engine controller. Distinct engine performance benefits that are realized from the use of variable cam phasing include an improvement in combustion stability at idle, improved airflow into the engine over a range of engine operations corresponding to improvements in engine performance, and improved dilution tolerance. This results in such benefits as improved fuel economy, improved torque at low engine speeds, lower engine cost and improved quality through elimination of external exhaust gas recirculation (EGR) systems, and improved control of engine exhaust emissions.
Performance of a fluid-driven actuator is reduced due to aeration of the fluid. The fluid is aerated by entrainment of air or by dissolving of air into the fluid. Dissolved and entrained air affects the physical properties of the fluid, including bulk modulus, or compressibility, and viscosity. When aerated fluid is pressurized, it increases in temperature at a greater rate than when not aerated. When the fluid is engine lubricating oil, this leads to reduction in oil lubricity and oil life. The aeration amount affects the performance of a pumping device to pump the fluid, in terms of pressure, flow and volumetric efficiency. It also affects the dynamic response of the pumping device. The amount of aeration also changes resonant frequency of the fluid, which affects response time and durability of a system that employs fluid to drive an actuator. There is a risk of increased of unacceptable noise levels and component-to-component interference when there is an unanticipated change in the dynamic response or resonant frequency of the system.
There are known engine operating characteristics that lead to aeration of the fluid. When the fluid is an engine lubricating oil, there is a sump in a crankcase of the engine. The engine lubricating oil is aerated as a result of rotating and reciprocating action of the crankshaft and piston rods into the sump and oil, and as a result of oil level in the sump being below a pump inlet pipe. The amount of aeration of the oil is measured and quantified for an engine that is operated under steady state operating conditions. The amount of aeration for a specific engine design is measured using a representative engine. This information is used by an engine control system to limit operation of the actuator, including implementation of algorithms that estimate an oil aeration amount based upon engine operation and time. In one example, an algorithm infers oil aeration by measuring an amount of time the engine spends within each of a number of engine speed ranges, including idle, off-idle to 1500 rpm, 1500-2000 rpm, and others. There are also algorithms that monitor both engine speed and engine temperature to determine oil aeration amount.
The engine control system uses information from an aeration algorithm to limit operation of the actuator, either by limiting the operating range or completely disabling the actuator when the oil aeration amount exceeds a threshold value. In either instance, the operator no longer derives any engine performance benefit from use of the actuator. A system that fails to employ some form of control based upon aeration of the oil risks loss of control of the actuator, which leads to degradation in functional performance and durability of the actuator and the base engine. Therefore, it is likely that a system designer will overestimate the amount of oil aeration, to protect the system and improve system and component durability. Again, the operator no longer derives any engine performance benefit from use of the actuator when it is disabled due to excessive oil aeration.
Each of these methods carries the disadvantage that it fails to account for a change in oil aeration amount associated with changes in attitude of the engine caused during dynamic operation. An engine in a vehicle experiences accelerations, decelerations, turning maneuvers, incline ascents and descents, and other actions that affect the fluid level and position in the sump, and therefore affect the interaction between the reciprocating parts of the engine and the oil. This action leads to more entrainment of air into the oil than was anticipated by the existing art, which compels a system designer to establish narrow actuator enable criteria.
The present invention provides an improvement over conventional engine controls that employ fluid-driven actuators in that it more accurately determines the amount of aeration of fluids such as engine oil, thus permitting more aggressive operation of the oil-driven actuator, with less limitations in scheduling operation of the actuator.
The present invention provides a method and a system for controlling a fluid-driven actuator used in an engine. This includes monitoring engine speed and fluid temperature, and determining a first and second attitude of the engine relative to a first and second axis. The invention then determines an amount of aeration of the fluid based upon those factors. The method determines an operating range of the fluid-driven actuator based upon the amount of aeration, and then permits the operation of the fluid-driven actuator within the operating range.
The present invention also encompasses monitoring an amount of agitation of the fluid directly, and determining the amount of aeration based upon the amount of agitation. The method then determines an operating range of the fluid-driven actuator based upon the amount of aeration, and allows operating the fluid-driven actuator within the operating range.
These and other objects of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the embodiments.